1. Field of the Invention
This invention relates to a grid that supports panels and ceiling fixtures in a suspended ceiling.
More particularly, the invention provides a compression relief section for controlled contraction of a main beam in the grid in the event of a fire.
2. Background Information
Grid beams in a suspended ceiling, under normal conditions, are subject only to vertical loads from panel and accessories. Hanger wires, anchored to the structural ceiling above the suspended ceiling, generally located 4xe2x80x2 apart on the main beams, provide support for such horizontal main beams. Cross beams are supported from the main beams. Both beams support panels. The beams are of an inverted T cross-section, and are formed by roll forming light sheet metal strip.
Under normal conditions, the beams are subject to primarily vertical loads. In the event of fire, however, the beams in the grid are subject to compressive forces in the manner of a column that supports a vertical load, although the load is applied horizontally at the ends of the beam. Under heat, the beam seeks to expand longitudinally, and since the ends are constrained at the walls of the room, the beams buckle, unless the build up of compression forces is relieved.
If the beams buckle, the panels are no longer supported in position, leaving the structural ceiling above the suspended ceiling exposed to the high heat of the fire. With the fire resistant panels in place, the structural ceiling is protected against the fire.
A prior art way of keeping the beams, which act as a horizontal column under a compressive load during a fire, relatively intact, is to provide in the beam relief joints that permit the beam to collapse longitudinally, while keeping the beam relatively straight. Such joints are shown, for instance, in U.S. Pat. Nos. 4,606,166 and 5,349,803, incorporated herein by reference.
The compression relief section of the invention has a notched channel in the web and a crushed and notched bulb. The section collapses and the beam contracts when the compression forces from a fire build-up in the beam. The section collapses in the manner wherein the channel, bulb, and flange of the beam fold in such a manner that the beam is kept longitudinally aligned, to provide support for the panels.